Outboard motor

ABSTRACT

An outboard motor includes an exhaust pipe that includes an outer wall section, an inner wall section, a coolant passage, and a constricted section. The inner wall section is arranged inward of the outer wall section. The coolant passage is arranged between the outer wall section and the inner wall section. The constricted section is configured to constrict a flow cross section of the coolant passage. A catalytic converter is housed in the exhaust pipe. A temperature sensor is installed in the constricted section and measures a temperature of a pipe wall of the exhaust pipe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an outboard motor.

2. Description of the Related Art

In recent years, outboard motors equipped with catalytic converters havebeen introduced to improve environmental performance. In outboard motorsequipped with catalytic converters, measures are taken to detectoverheating of an exhaust pipe in order to prevent the catalyticconverter from being damaged by heat. When overheating is detected, acontrol is executed to forcefully stop the engine or to issue a warningthrough an indicator device to inform a driver. In response, the driverthen performs an inspection to eliminate the overheating.

When detecting overheating in this way, if incorrect detections ofoverheating occur frequently, then the detections will become bothersomefor a driver who must conduct an inspection every time overheating isdetected. Therefore, there is a demand for preventing incorrectdetections of overheating. For example, Laid-open Japanese PatentApplication No. 11-101172 discloses a watercraft engine exhaustapparatus equipped with an exhaust gas temperature sensor and an exhaustpipe temperature sensor. The exhaust gas temperature sensor measures atemperature of an exhaust gas at a position downstream of a catalyticconverter. The exhaust pipe temperature sensor measures a temperature ofa pipe wall of the exhaust pipe at a position downstream of thecatalytic converter. Incorrect detections are prevented by detectingoverheating using detection signals from both the exhaust gastemperature sensor and the exhaust pipe temperature sensor.

SUMMARY OF THE INVENTION

However, with the exhaust apparatus presented in Laid-open JapanesePatent Application No. 11-101172, the number of parts is larger and,thus, the cost is higher because two sensors, i.e., an exhaust gastemperature sensor and an exhaust pipe temperature sensor, must beprovided in order to prevent an incorrect detection.

Accordingly, preferred embodiments of the present invention provide anoutboard motor that prevents incorrect detections of overheating whilealso preventing an increase in the number of parts.

An outboard motor according to a preferred embodiment of the presentinvention includes an engine, an exhaust manifold, an exhaust pipe, acatalytic converter, and a temperature sensor. The engine includes aplurality of cylinders, a plurality of exhaust ports, and a crankshaft.The cylinders are arranged side-by-side above and below one another. Theexhaust ports are provided on the cylinders, respectively. Thecrankshaft is arranged to extend in a vertical direction. The exhaustmanifold is connected to the exhaust ports. The exhaust pipe isconnected to the exhaust manifold. The exhaust pipe includes an outerwall section, and inner wall section, a coolant passage, and aconstricted section. The inner wall section is arranged inward of theouter wall section. The coolant passage is arranged between the outerwall section and the inner wall section. The constricted section isconfigured to constrict a flow cross section of the coolant passage. Thecatalytic converter is housed in the exhaust pipe. The temperaturesensor is installed in the constricted section. The temperature sensoris configured to measure a temperature of a pipe wall of the exhaustpipe.

In an outboard motor according to this preferred embodiment of thepresent invention, the temperature sensor is installed in theconstricted section of the exhaust pipe. At the constricted section, aflow speed of a coolant is faster because the coolant passage isnarrower. Thus, when a flow rate of the coolant in the coolant passagechanges, the temperature of the constricted section changes markedly.Consequently, overheating can be detected accurately by arranging forthe temperature sensor to measure a temperature of the pipe wall at theconstricted section of the exhaust pipe. As a result, incorrectdetections of overheating can be significantly reduced while preventingan increase in the number of parts

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an outboard motor according to a preferredembodiment of the present invention.

FIG. 2 is a rear view of the outboard motor.

FIG. 3 is a side view of an engine unit.

FIG. 4 is a sectional view taken along a section line IV-IV of FIG. 1.

FIG. 5 is a sectional view taken along a section line V-V of FIG. 1.

FIG. 6 is a sectional view taken along a section line VI-VI of FIG. 2.

FIG. 7 is a side view of a catalytic converter unit.

FIG. 8 is a frontal view of the catalytic converter unit.

FIG. 9 is a top plan view of the catalytic converter unit.

FIGS. 10A and 10B are sectional views of the catalytic converter unit.

FIGS. 11A-11C are sectional views of the catalytic converter unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a side view of an outboard motor 1 according to a preferredembodiment of the present invention. FIG. 2 is a rear view of theoutboard motor 1. As shown in FIG. 1 and FIG. 2, the outboard motor 1includes an upper casing 2, a lower casing 3, an exhaust guide section4, and an engine unit 5. In FIG. 1 and FIG. 2, the upper casing 2 isdepicted in a cross sectional view in order to facilitate understanding.The upper casing 2, the lower casing 3, and the engine unit 5 are fixedto the exhaust guide section 4.

The engine unit 5 is arranged inside the upper casing 2. The engine unit5 includes an engine 6. As shown in FIG. 1, a drive shaft 11 is arrangedinside the lower casing 3. The drive shaft 11 is arranged along avertical direction inside the lower casing 3. The drive shaft 11 isfixed to a crankshaft 26 of the engine 6. A propeller 12 is arranged ona lower portion of the lower casing 3. The propeller 12 is arrangedbelow the engine 6. The propeller 12 includes a propeller boss 13. Apropeller shaft 14 is arranged inside the propeller boss 13. Thepropeller shaft 14 is arranged to extend along a longitudinal direction(front-back direction). The propeller shaft 14 is coupled to a lowerportion of the drive shaft 11 through a bevel gear 15.

In the outboard motor 1, a drive force generated by the engine 6 istransmitted to the propeller 12 through the drive shaft 11 and thepropeller shaft 14. As a result, the propeller 12 is rotated in aforward direction or a reverse direction. In this way, a propulsionforce is generated which propels a watercraft hull to which the outboardmotor 1 is attached forward or backward.

As shown in FIG. 1, the outboard motor 1 includes an exhaust passage 16.The exhaust passage 16 is arranged such that it extends from the engine6 to the propeller boss 13 of the propeller 12 through the insides ofthe exhaust guide section 4 and the lower casing 3. Exhaust gasdischarged from the engine 6 passes from the exhaust passage 16 to thewater through an inside of the propeller boss 13.

FIG. 3 is a side view of the engine unit 5. As shown in FIG. 3, theengine 6 includes a cylinder block 21, a cylinder head 22, and acrankcase 23. The cylinder block 21 is arranged on the exhaust guidesection 4 and is fixed to the exhaust guide 4. FIG. 4 is a sectionalview of the outboard motor 1 taken along a section line IV-IV of FIG. 1.As shown in FIG. 4, the cylinder block 21 includes four cylinders 21 ato 21 d. The four cylinders 21 a to 21 d are arranged side-by-side aboveand below one another.

As shown in FIG. 3, the cylinder head 22 is arranged rearward of thecylinder block 21. FIG. 5 is a sectional view of the outboard motor 1taken along a section line V-V of FIG. 1. As shown in FIG. 5, intakeports 24 a to 24 d and exhaust ports 25 a to 25 d are disposed insidethe cylinder head 22. Each of the intake ports 24 a to 24 d and each ofthe exhaust ports 25 a to 25 d are connected to one of the cylinders 21a to 21 d, respectively. The intake ports 24 a to 24 d are arrangedvertically above and below one another. The intake ports 24 a to 24 dare connected to a fuel supplying device not shown in the drawings. Theexhaust ports 25 a to 25 d are arranged vertically above and below oneanother. The exhaust ports 25 a to 25 d extend in a lateral directionand connected to an exhaust manifold 31 explained later.

As shown in FIG. 3, the crankcase 23 is arranged frontward of thecylinder block 21. The crankshaft 26 (see FIG. 1) is arranged inside thecrankcase 23. The crankshaft 26 extends along a vertical direction. Anupper end portion of the drive shaft 11 is connected to a lower endportion of the crankshaft 26. Movement of pistons (not shown) arrangedinside the cylinders 21 a to 21 d is transmitted to the drive shaft 11through the crankshaft 26.

As shown in FIG. 3, the engine unit 5 includes the exhaust manifold 31.The exhaust manifold 31 is arranged laterally of the cylinder head 22and on a side of the engine. The exhaust manifold 31 is preferablyformed as an integral portion of the cylinder head 22. The exhaustmanifold 31 is arranged to extend along a vertical direction. As shownin FIG. 5, a plurality of openings 36 a to 36 d are provided in theexhaust manifold 31 and the exhaust manifold 31 connects to the exhaustports 25 a to 25 d through the openings 36 a to 36 d, respectively.Exhaust gas discharged from the exhaust ports 25 a to 25 d collects inthe exhaust manifold 31. The exhaust manifold 31 includes a firstopening 33. The first opening 33 is positioned between the cylinder 21 apositioned highest and the cylinder 21 d positioned lowest among theplurality of cylinders 21 a to 21 d.

As shown in FIG. 3, the engine unit 5 includes a catalytic converter 32.As shown in FIG. 4 and FIG. 6, the catalytic converter unit 32 includesa catalyst member 44 and a catalyst housing pipe 45. The catalyst member44 is arranged in the exhaust passage 16 inside the catalyst housingpipe 45. The catalyst housing pipe 45 is an example of the “exhaustpipe” according to a preferred embodiment of the present invention. Thecatalytic converter unit 32 is arranged laterally of the engine 6. Thus,the catalyst member 44 is arranged laterally of the engine 6. Morespecifically, the catalyst member 44 is positioned higher than a loweredge portion of the cylinder 21 d, which is positioned lowest among thefour cylinders 21 a to 21 d. The catalyst housing pipe 45 is arrangedhorizontally side-by-side with respect to the exhaust manifold 31. Thecatalyst housing pipe 45 is arranged to extend in a vertical direction.An end of the catalyst housing pipe 45 is connected to the first opening33 of the exhaust manifold 31. Another end of the catalytic converterpipe 45 is connected to a second opening 54 of the cylinder block 21(explained later). The catalyst member 44 supports a catalyst serving toclean exhaust gas. The catalyst preferably is, for example, a three-waycatalyst. The catalyst member 44 preferably is a cylindrically shapedmember having a honeycomb structure, for example. Exhaust gas flows fromabove to below through the catalyst member 44. The exhaust gas passingthrough the exhaust passage 16 is cleaned as it passes through thecatalyst member 44 inside the catalyst housing pipe 45. The structure ofthe catalytic converter unit 32 will be explained in more detail later.

The exhaust manifold 31 and the catalytic converter unit 32 define aportion of the exhaust passage 16. The exhaust passage 16 also includesa first lower passage 51, a second lower passage 52, and a third lowerpassage 53. The first lower passage 51 is located inside the cylinderblock 21. The first lower passage 51 includes a second opening 54. Thesecond opening 54 is located in a lower portion of a side surface of thecylinder block 21. The first lower passage 51 is connected to thecatalytic converter unit 32 through the second opening 54. The secondlower passage 52 is located inside the exhaust guide section 4. As shownin FIG. 4 and FIG. 6, the second lower passage 52 is connected to thefirst lower passage 51. As shown in FIG. 1, the third lower passage 53is located inside the lower casing 3. The third lower passage 53 isconnected to the second lower passage 52. The third lower passage 53 isalso connected to the propeller boss 13.

In the outboard motor 1 according to this preferred embodiment, exhaustgas discharged from the cylinders 21 a to 21 d is guided from thecylinders 21 a to 21 d to underneath the engine 6 by the exhaust passage16. More specifically, exhaust gas from the exhaust ports 25 a to 25 dof the engine 6 collects in the exhaust manifold 31. The exhaust gasflows from the exhaust manifold 31 to the catalytic converter unit 32.The exhaust gas is cleaned as it passes through the catalyst member 44in the catalytic converter unit 32. The exhaust gas then passes throughthe first lower passage 51, the second lower passage 52, the third lowerpassage 53, and the inside of the propeller boss 13 and is discharged tothe outside.

As shown in FIG. 3 and FIG. 4, the catalytic converter unit 32 isequipped with a first oxygen sensor 55 and a second oxygen sensor 56 todetect an oxygen concentration of the exhaust gas. The first oxygensensor 55 is arranged upstream of the catalyst member 44 inside theexhaust passage 16. More specifically, the first oxygen sensor 55 isarranged above the catalyst member 44 inside the catalyst housing pipe45. The second oxygen sensor 56 is arranged below the catalyst member 44inside the catalyst housing pipe 45. The second oxygen sensor 56 isarranged downstream of the catalyst member 44 inside the exhaust passage16. Detection signals from the first oxygen sensor 55 and the secondoxygen sensor 56 are fed to an ECU not shown in the drawings. The ECUcontrols the engine 6 based on detection values from the first oxygensensor 55 and the second oxygen sensor 56.

The structure of the catalytic converter unit 32 will now be explainedin more detail. FIG. 7 is a side view of the catalytic converter unit32. FIG. 8 is a frontal view of the catalytic converter unit 32. FIG. 9is a top plan view of the catalytic converter unit 32.

The catalyst housing pipe 45 includes a first curved section 46, astraight section 47, and a second curved section 48. The first curvedsection 46 is configured to curve toward the first opening 33 of theexhaust manifold 31. The straight section 47 is configured to extendstraight in a vertical direction. The straight section 47 is arrangedbelow the first curved section 46. The catalyst member 44 is arrangedinside the straight section 47. The second curved section 48 is arrangedbelow the straight section 47. The second curved section 48 isconfigured to curve toward the second opening 54 of the cylinder block21. As shown in FIG. 9, the catalyst housing pipe 45 includes a firstside surface 58 that faces the engine 6 and a second side surface 59that is farther from the engine 6 than the first side surface 58. Atemperature sensor 61 is installed in the second side surface 59 of thecatalyst housing pipe 45. The temperature sensor 61 measures atemperature of a pipe wall of the catalyst housing pipe 45. The ECU (notshown in the drawings) determines if overheating of the engine 6 isoccurring based on a detection value of the temperature sensor 61. Thefirst oxygen sensor 55 is installed in the second side surface 59 of thecatalyst housing pipe 45.

FIG. 10A is a sectional view taken along a section line AA-AA of FIG. 7.FIG. 10B is a sectional view taken along a section line AB-AB of FIG. 7.FIG. 11A is a sectional view taken along a section line BA-BA of FIG. 7.FIG. 11B is a sectional view taken along a section line BB-BB of FIG. 7.FIG. 11C is a sectional view taken along a section line BC-BC of FIG. 7.As shown in FIGS. 10A, 10B and FIGS. 11A-11C, the catalytic housing pipe45 includes an outer wall section 62, an inner wall section 63, and acoolant passage 64. The inner wall section 63 is arranged inward of theouter wall section 62. The coolant passage 64 is arranged between theouter wall section 62 and the inner wall section 63. A coolant flowsthrough the coolant passage 64. The catalytic converter unit 32 iscooled by the coolant in the coolant passage 64. As shown in FIG. 6,coolant passages 64 are also provided inside the cylinder block 21 andthe exhaust manifold 31. The coolant passage 64 of catalytic converterunit 32 communicates with the coolant passage 64 of the cylinder block21 and the coolant passage 64 of the exhaust manifold 31.

As shown in FIG. 10A, FIG. 11A, and FIG. 11B, the catalyst housing pipe45 includes a constricted section 65. The constricted section 65 is aportion of the catalyst housing pipe 45 where the coolant passage 64 isnot provided and constitutes a rib connecting the inner wall section 63and the outer wall section 62 together. Consequently, a flow crosssection of the coolant passage 64 is reduced at the constricted section65. In other words, the constricted section 65 constricts the flow crosssection of the coolant passage 64. As shown in FIG. 9, the constrictedsection 65 is provided at the second side surfaces 59. The constrictedsection 65 is also provided at the first curved section 46. Therefore,the constricted section 65 is arranged upstream of the catalyst member44 in the catalyst housing pipe 45. The constricted section 65 ispositioned above the catalyst member 44.

The constricted section 65 includes a protruding section 66 and a hole67 (see FIG. 11A). As shown in FIG. 9, the protruding section 66protrudes outward of the catalyst housing pipe 45 from an externalsurface of the catalyst housing pipe 45. The protruding section 66includes a flat surface 66 a. As shown in FIG. 10A, a hole 66 b isformed in the flat surface 66 a. The hole 66 b is configured to recedeinward toward the inside of the catalyst housing pipe 45 from the flatsurface 66 a. The hole 66 b does not communicate with the exhaustpassage 16 inside the catalyst housing pipe 45 and a bottom of the hole66 b is closed. The temperature sensor 61 is installed in the hole 66 bof the flat surface 66 a. As shown in FIG. 11B, a thickness of thecatalyst housing pipe 45 at the protruding section 66 is larger than athickness of the catalyst housing pipe 45 at other portions.

As shown in FIG. 11A, the hole 67 communicates with the exhaust passage16 inside the catalyst housing pipe 45. The first oxygen sensor 55 isinstalled in the hole 67 of the constricted section 65. As shown in FIG.7, the second curved section 48 includes a hole 68 similar to the hole67 of the first curved section 46. As shown in FIG. 3, the second oxygensensor 56 is installed in the hole 68 of the second curved section 48.

In the outboard motor 1 according to this preferred embodiment, thetemperature sensor 61 is preferably installed in the constricted section65 of the catalyst housing pipe 45. At the constricted section 65, aflow speed of the coolant is faster because the coolant passage 64 isnarrower. Thus, when a flow rate of the coolant in the coolant passage64 changes, the temperature of the constricted section 65 changesmarkedly. Consequently, overheating can be detected accurately byarranging for the temperature sensor 61 to measure a temperature of thepipe wall at the constricted section 65 of the catalyst housing pipe 45.As a result, incorrect detections of overheating can be significantlyreduced while preventing an increase in the number of parts.

Since the first oxygen sensor 55 is inserted inside the exhaust passage16, it is necessary to provide a hole 67 that passes through the wallportion of the catalyst housing pipe 45 in order to install the firstoxygen sensor 55 in the catalyst housing pipe 45. Since the coolantpassage 64 is not arranged in the constricted section 65, the hole 67can easily be formed such that it passes through to the exhaust passage16 inside the catalyst housing pipe 45. Thus, the constricted section 65can also serve as a mounting section for the temperature sensor 61 and amounting section for the first oxygen sensor 55.

Since the constricted section 65 is a rib connecting the inner wallsection 63 and the outer wall section 62, the thickness of the catalysthousing pipe 45 at the constricted section 65 is larger than thethickness of the catalyst housing pipe 45 at other portions.Consequently, the thermal capacity of the constricted section 65 islarger than the thermal capacity of the other portions and a decline inthe resistance to heat can be prevented even though the coolant passage64 is not provided in the constricted section 65.

The constricted section 65 is preferably provided at the first curvedsection 46. Since the exhaust passage 16 is curved at the first curvedsection 46, the exhaust gas readily strikes against the constrictedsection 65. Consequently, the temperature sensor 61 can measure atemperature of the pipe wall accurately.

The constricted section 65 is preferably provided at the second sidesurface 59 of the catalyst housing pipe 45. Consequently, the catalyticconverter unit 32 can be arranged closer to the engine 6 than if theconstricted section 65 were provided at the first side surface 58. As aresult, the engine 6 and the catalytic converter 32 can be arranged in amore compact fashion.

Although a preferred embodiment of the present invention has beendescribed above, the present invention is not limited to the preferredembodiment described above. Various changes can be made withoutdeparting from the scope of the present invention.

The number of cylinders is not limited to four. Having three or fewercylinders is also acceptable. It is also acceptable to have five or morecylinders. Although in the previously explained preferred embodiment,the constricted section 65 is preferably provided at the first curvedsection 46, it is also acceptable to provide the constricted section 65at the straight section 47 or another portion, for example. Although inthe previously explained preferred embodiment, the constricted section65 is preferably provided at the second side surface 59 of the catalysthousing pipe 45, it is also acceptable to provide the constrictedsection 65 at the first side surface 58. However, as explainedpreviously, it is preferable to provide the constricted section 65 atthe second side surface 59 from the standpoint of arranging the engine 6and the catalytic converter unit 32 in a compact fashion. It is alsoacceptable to provide the constricted section 65 at a front surface ofthe catalyst housing pipe 45.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An outboard motor comprising: an engine includinga plurality of cylinders arranged side-by-side above and below oneanother, a plurality of exhaust ports provided on the plurality ofcylinders, and a crankshaft extending in a vertical direction; anexhaust manifold connected to the exhaust ports; an exhaust pipeconnected to the exhaust manifold, the exhaust pipe including an outerwall section, an inner wall section located inward of the outer wallsection, a coolant passage located between the outer wall section andthe inner wall section, and a constricted section that constricts a flowcross-section of the coolant passage; a catalytic converter housed inthe exhaust pipe; and a temperature sensor located in the constrictedsection to measure a temperature of a pipe wall of the exhaust pipe;wherein the constricted section is a rib that connects the inner wallsection and the outer wall section together.
 2. The outboard motoraccording to claim 1, further comprising: an oxygen sensor that detectsan oxygen concentration of exhaust gas from the exhaust ports; whereinthe constricted section includes a hole that passes through to an insideof the exhaust pipe; and the oxygen sensor is located in the hole of theconstricted section.
 3. The outboard motor according to claim 1, whereinthe exhaust pipe includes a curved section having a curved shape and theconstricted section is provided at the curved section.
 4. The outboardmotor according to claim 1, wherein the exhaust pipe is locatedlaterally relative to the engine; the exhaust pipe includes a first sidesurface that faces the engine and a second side surface that is fartheraway from the engine than the first side surface; and the constrictedsection is located at the second side surface.
 5. The outboard motoraccording to claim 1, wherein the constricted section is upstream of thecatalytic converter in the exhaust pipe.